GraphQL Federation

gistfile1.js

// Service A

const resolvers = {
  User: {
    id(parent) {
      return parent.Id;
    },
  },
};

const typeDefs = gql`
  interface Node {
    id: ID!
  }
  type User implements Node @key(fields: "id") {
    id: ID!
    internalId: ID!
    type: String!
  }
`;

const server = new ApolloServer({
  schema: buildFederatedSchema([
    {
      typeDefs,
      resolvers,
    },
  ]),
});


// Service B

const typeDefs = gql`
  extend type Query {
    me: User
  }

  extend type User @key(fields: "id") {
    id: ID! @external
    name: String
    username: String
  }
`;

const resolvers = {
  Query: {
    me() {
      return { id: 'RW1wbG95ZWU6MjA2NDIy', name: 'Matt Myers', username: 'mmyers' };
    },
  },
};

const server = new ApolloServer({
  schema: buildFederatedSchema([
    {
      typeDefs,
      resolvers,
    },
  ]),
});

Then doing:

query {
  me {
    name
  }
}

And get the following error: GraphQLError: Unknown type "_Any".
And: Cannot query field "_entities" on type "Query".

Just updated gist with the latest. No longer getting errors, but it's not returning the name. Ideas? I'm getting close.

I got it working. Thanks so much!

Edit: Oops, seems like you figured it out on your own. Here's my findings anyway 😄

Hi @ziplizard, I've managed to get this working:
Service A

const resolvers = { };

const typeDefs = gql`
  interface Node {
    id: ID!
  }
  type User implements Node @key(fields: "id") {
    id: ID!
    internalId: ID!
    type: String!
  }
`;

Service B

const typeDefs = gql`
  extend type Query {
    me: User
  }
  extend type User @key(fields: "id") {
    id: ID! @external
    name: String
    username: String
  }
`;

const resolvers = {
  Query: {
    me() {
      return { id: 'RW1wbG95ZWU6MjA2NDIy'  };
    },
  },
  User: {
    __resolveReference(object) {
      // find user by id
      if (object.id === 'RW1wbG95ZWU6MjA2NDIy') {
        return {
          ...object,
          name: 'Matt Myers',
          username: 'mmyers'
        }
      }
    }
  }
};

I think the key is providing User.__resolveReference in every service that adds fields to User. Notice how I didn't include it in Service A though because in that service User only has id. If it has more fields that were not included in the key I believe you would need to include User.__resolveReference in that resolver as well.